カテコールアミンのラジオレセプターアッセイ

概要

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We established a radioreceptor assay for catecholamines (CA), utilizing the microsomal fraction of bovine myocardium as CA receptors and 3H-norepinephrine (3H-NA) as a ligand. Since 3H-NA binding to the prepared CA binding protein was inhibited by alpha-adrenergic blocking agents, the CA receptors used were assumed to be alpha-adrenergic receptors. In this paper, we studied binding sites of CA to alpha-adrenergic receptors by a displacement study using such compounds as CA, CA metabolites, substances of dihydroxytetrahydronaphthalene derivatives, and other compounds. Various compounds with catechol nucleus had an affinity to the CA binding protein. The displacement study with compounds of dihydroxytetrahydronaphthalene derivatives revealed that compounds which were capable of binding to alpha-adrenoceptors had 2 neighbouring phenol groups in the benzen ring at either position 2 and 3, or at position 3 and 4. On the other hand, either phenylalanine or tyrosine, which has only one phenol group in the benzen ring, did not bind the receptors. It is conceivable, therefore, that the binding sites of CA to alpha-adrenergic receptors is position 2 to 4 of the catechol nucleus, where 2 neighbouring phenol groups exist.